The purpose of this study is to treat patients with recurrent malignant gliomas using continuous infusion phenylacetate acid at a dose of 400 mg/kg/day for fourteen days every two weeks. The study end-points are toxicity, response rates, and time to treatment failure. All patients will be followed for survival. Sufficient accrual will occur to determine if phenylacetate, using this dose schedule, produces a true response or stabilization rate of greater than 20 percent, as well as improvement in time to progression. This is an open-label, multicenter Phase II study of phenylacetic acid (PAA) in patients with recurrent malignant glioma. PAA will be administered through an infusion pump as a continuous 24-hour infusion at a starting dose of 400 mg/kg/day for fourteen days followed by a fourteen day rest period and then a repeat course of the drug. This will constitute a single cycle. Tumor evaluations will be performed prior to each cycle.